1. Field of the Invention
The present invention is concerned with a new process for preparing 4-oxo-4H-pyran-3-carboxamide compounds, which are useful for medicines or pesticides, or intermediates thereof.
2. Description of the Prior Arts
There have been reported some methods for preparing 4-oxo-4H-pyran-3-carboxamide compounds concerning this invention. That is, A. Mellams et al reported that the treatment of certain acetoacetanilide derivatives with polyphosphoric acid under heating gave the corresponding 2,6-dimethyl-4-oxo-4H-pyran-3-carboxamides [cf., J. Org. Chem., 29, 3548 and 3555 (1964)]. R. Garner et al [cf., J. Chem. Soc. (c), 186(1966)] stated that Mellams et al' report was specific to certain acetoacetanilide derivatives having electron widthdrawing substituents and when acetoacetanilide itself was used in the reaction, it gave 2-hydroxyquinoline derivative but did not form the pyrone compound.
Japanese Patent Publication No. Sho 45(1970)-31,663 disclosed a method for reacting isocyanates with diketene in the presence of an acid catalyst, to yield 3,4-dihydro-2,4-dioxo-6-methyl-2H-1,3-oxazines and/or 2,6-dimethyl-4-oxo-4H-pyran-3-carboxamides (stated as 3-carbamyl-2,6-dimethyl-4-pyrones in this publication). In this reaction, the latter 2,6-dimethyl-4-oxo-4H-pyran-3-carboxamides are observed to be predominantly formed when ortho substituted compounds such as o-chlorophenylisocyanate or o-nitrophenylisocyanate, or meta substituted compounds such as m-nitrophenylisocyanate were used. This method would be effective in cases where the starting materials of isocyanates are easily available, but would be not generally applicable to any of isocyanates because reaction selectivity is largely influenced by their structure.
It has also been known that 2,6-dimethyl-4-oxo-4H-pyran-3-carboxamide compounds could be obtained by the reaction of diketene and primary arylamines, such as aniline derivatives, aminotropolones or aminopyridines.
Kato et al [cf., Yakugakuzassi, 87, 1212(1967)] reported that the reaction of diketene and aniline derivatives in the presence of a basic catalyst gave pyridone type rings, except that the use of p-nitroaniline gave 2,6-dimethyl-N-(4-nitrophenyl)-4-oxo-4H-pyran-3-carboxamide.
H. Toda et al [cf., Chem. Pharm. Bull., 19 1477(1971)] reported on the reaction between aminotropones and diketene, where the use of 4-aminotropolone and 2-aminotropone gave 4-pyrone compounds, and the use of 5-aminotropolone gave a pyridonetype ring closed compound. Kato et al [Chem. Pharm. Bull., 20 133(1972)] also reported that 2-amino- or 4-aminopyridine derivatives gave mainly 4-pyrone compounds, while 3-aminopyridine derivatives gave mainly pyridone type compounds.
The reactivity of heterocyclic amines was reported in J. Heterocyclic Chem., 13, 291(1976) by R. F. Lauer et al where 2-amino-1,3,4-thiadiazole gave a 4-pyrone compound, although its yield is unclear.
As is clear from the above statement, the reaction selectivity between diketene and primary arylamines is greatly influenced by the structure of the arylamines to be used. Therefore, it was previously impossible to predominantly yield 4-pyrone compounds as far as primary arylamines are used.
Similarly, it has been reported that the treatment of acetoacetyl derivatives of arylamines with diketene yielded either pyridone compounds or 4-pyrone compounds, depending upon the structure of said starting materials. It is especially mentioned that with N-methylaniline as a secondary arylamine it is impossible to form pyridone ring closure. This reaction gave 4-pyrone compound with approximately quantitative yield, when a quaternary ammonium chloride is used as a catalyst [cf., E. V. Dehmlow & A. R. Shamout., Liebigs Ann. Chem., 2062(1982)].
In addition, the reaction for obtaining an 4-pyrone compound from 2,2,6-trimethyl-1,3-dioxin-4-one has been known. That is, T. Kato et al [Chem, Pharm. Bull., 30, 1315(1982)] studied on the reaction between amides or acetoacetyl derivatives thereof and 2,2,6-trimethyl-1,3-dioxin-4-one and reported that the reaction of N-formylacetoacetamide with 2,2,6-trimethyl-1,3-dioxin-4-one in the presence of N,N-dimethylaniline gave a pyridone compound as the main product and 4-pyrone compound as the by-product.
The known methods for preparing 4-oxo-4H-pyran-3-carboxamide compounds as described above show as a common feature that the selectivity in reaction is influenced by the structure of the starting materials, and cannot generally apply to any of the starting materials. As a method to avoid such difficulty, Kato et al [Yakugakuzassi, 101, 40(1981)] reported that the reaction of 3-morpholinocrotonanilide derivatives and diketene under heating gave the corresponding 4-pyronecompounds, in which change in structure of 3-morpholinocroton anilide derivatives is assumed not to give any serious influence on yield. This method however yielded a mixture with pyridone compounds when 3-benzylaminocrotonanilide derivatives are used.
Thus, the present invention has been completed on the basis of observation which is different from the result predicted from the above known facts and provides a generally applicable method for preparing 4-oxo-4H-pyran-3-carboxamide compounds.